Magnetic recording medium and a process of fabricating such magnetic recording medium

Abstract

A magnetic recording medium comprising a support and provided thereon a magnetic layer containing magnetic powder and a copolymer capable of being soluble in water by 10 parts by weight or more per 100 parts by weight of water. Further, a process of preparing a magnetic recording medium wherein magnetic powder is treated with a copolymer capable of dissolving 10 parts by weight or more per 100 parts by weight of water in an aqueous medium under presence of a metal ion and a magnetic paint containing this treated magnetic powder is coated on base to form a magnetic layer is also provided. Further a process of preparing a magnetic recording medium wherein magnetic powder emulsion that has been pretreated for a higher coercive force is filtered to separate unnecessary materials from magnetic powder and said magnetic powder is surface treated in an aqueous medium with a copolymer capable dissolving 10 parts by weight or more per 100 parts by weight of water, and a magnetic paint comprising this surface treated magnetic powder is coated on base to form a magnetic layer.

What is claimed is: 
     
       1. A magnetic recording medium comprising a support and a magnetic layer thereon, said magnetic layer being formed by coating said support with a magnetic paint comprising (a) an organic solvent,   (b) an organic binder, and   (c) a magnetic powder, said magnetic powder being pre-treated with a copolymer containing at least one monomer component having an anionoid organic group in the form of a salt and a second monomer component, said copolymer being capable of being dissolved in water in an amount of at least 10 parts by weight of said copolymer per 100 parts by weight of water.     
     
     
       2. The medium of claim 1, wherein the polymerization degree of said copolymer, expressed as the total number of monomer units contained within said copolymer, is up to 100. 
     
     
       3. A magnetic recording medium as claimed in claim 1 wherein said anionoid organic group or groups are carboxyl groups. 
     
     
       4. A magnetic recording medium as claimed in claim 4 wherein said monomer component is an alkylene with a plurality of carboxyl groups attached to carbon atoms comprising the main molecular chain of said alkylene. 
     
     
       5. A magnetic recording medium as claimed in claim 1 wherein the other monomer component or components are alkylenes of branched chain having 4 or more carbon atoms. 
     
     
       6. A magnetic recording medium as claimed in claim 1 wherein said magnetic powder has a specific surface area (BET value) of 30 m 2  /g or over. 
     
     
       7. A magnetic recording medium as claimed in claim 1 wherein said magnetic layer contains a soft polyurethane having a tensile strength less than 200 kg/cm 2  and breaking elongation of 900% or over, hard polyurethane having a tensile strength of 200 kg/cm 2  or over and breaking elongation below 900%, and magnetic powder pretreated with a copolymer that comprises one or more monomer component having an anionoid organic group or groups in the form of salt. 
     
     
       8. The process of claim 7 wherein the degree of polymerization of said copolymer, as expressed by the total number of monomer units contained within said copolymer, is up to 100. 
     
     
       9. A process of preparing a magnetic recording medium comprising (i) treating a magnetic powder in an aqueous or hydrophilic medium with a copolymer which contains at least 1 monomer component having an anionoid organic group in the form of a salt and a second monomer component, said copolymer capable of being dissolved in water in an amount of at least 10 parts by weight of said copolymer in 100 parts by weight of water,   (ii) separating said treated magnetic powder from said aqueous or hydrophilic medium,   (iii) drying said treated magnetic powder,   (iv) preparing a magnetic paint comprising said treated magnetic powder, an organic binder, and an organic solvent, and   (v) coating said magnetic paint on a support to form said magnetic recording medium.   
     
     
       10. A process as claimed in claim 9 wherein said magnetic powder is treated with said copolymer in said aqueous medium adjusted to a pH of 7 or more. 
     
     
       11. A process as claimed in claim 9 wherein after said magnetic powder is treated with said copolymer the treated magnetic powder is further immersed in liquid organic substance under presence of an oxidative gas and if necessary then dried under presence of an oxidative gas. 
     
     
       12. A process as claimed in claim 9 wherein said anionoid groups are carboxyl groups. 
     
     
       13. A process as claimed in claim 12 wherein said monomer component is an alkylene having a plurality of carboxyl groups in the main chain thereof. 
     
     
       14. A process as claimed in claim 9 wherein the other monomer component or components of said copolymer is a branched chain alkylene having 4 or more carbon atoms.